The present invention relates to a method of operating a torque transfer system in a motor vehicle, and it also relates to a torque transfer system that is capable of operating according to the inventive method.
A torque transfer system in the sense of the present invention is an arrangement with the capability to convert a characteristic rotary quantity of an input shaft into an either identical or different rotary quantity of an output shaft and/or with the capability to couple and uncouple the input shaft and the output shaft. As the term is used in the present context, a torque transfer system can include a clutch device and/or transmission device and/or a torque converter device or any other mechanism in the same general category.
A characteristic rotary quantity is used to characterize the dynamic situation of a rotating part, particularly a shaft. Specific examples of characteristic rotary quantities are a torque or an rpm rate.
A transmission device in the sense of the present invention is a mechanism that can be shifted in steps or in a continuous, step-less range, into different shift positions corresponding to different transmission ratios between two shafts of the transmission device. The transmission device can be shifted automatically or manually, or in a partially automatic or automated mode with the possibility of manual intervention.
A transmission device in the sense of the present invention encompasses in particular manually operated step-shifting transmissions, or cone-pulley transmissions, or automatic transmissions. An automatic transmission is a transmission device in which the shifts are controlled automatically and occur without interruption in the tractive force, specifically with a planetary gear mechanism. The transmission in the present context is configured in particular as an automated shift transmission. The term xe2x80x9cautomated shift transmissionxe2x80x9d relates to a transmission device in which the shift movements are automated, but are accompanied by an interruption in vehicle traction.
A clutch device in the sense of the present invention may be configured with or without power branching and can include a start-up clutch, a friction clutch, a reverse-gear clutch, a laminar disc clutch, a magnet-powder clutch, a converter bypass clutch, or another device of the same general category.
With special preference, the clutch is configured as an electronically controlled clutch device in which the movement between different positions of the clutch can be performed under electronic control. An electronically controlled clutch device has been described by and is available from the assignee of the present invention under the name xe2x80x9cElectronic Clutch Management (ECM)xe2x80x9d.
In particular, an electronically controlled clutch device of the foregoing description has the capability of operating in a crawl mode.
A crawl mode in the sense of the present invention is an operating mode where the clutch is held in a position to transmit a predetermined amount of crawl torque. A crawl torque in the present context means in essence a small amount of torque that is transmitted through the clutch, e.g., while the engine is running, the brake is not applied, and the gas pedal or other fuel-metering device is being actuated. The crawl torque is transmitted also when a gear is set in the transmission of the motor vehicle. In particular, a crawl mode is controlled by a control device in accordance with a predetermined characteristic which can include mathematical functions, curve fields, or other functional relationships.
A transmission device in the sense of the present invention includes in particular a control device, an actuating device, and a shifting device. The shifting device has at least two movable elements, in particular a shifter finger as a first shifter element, and a shifter shaft or shifter fork as a second shifter element.
The first shifter element can be moved in a shift gate arrangement with at least one selector track and at least one shift track. The selector track and the shift tracks in the sense of the present invention may be real or virtual tracks. A virtual track means that the movement of the first shifter element is not constrained by physical guide barriers, but is nevertheless limited within certain track-like paths. The limitations or constraints on the movement may be realized by elements that are coupled to the first shifter element. The arrangement may include travel-delimiting devices which can be part of a control device or an actuating device.
The shift gate arrangement can have a configuration where the shift tracks join the selector track at right angles. In particular, the shift gate arrangement may be configured with three or four parallel shift tracks that meet the selector track at different selector positions.
A shift track in the sense of the present invention consists either of one branch that runs in one direction from a selector position on the selector track, or two branches that run in opposite directions from a selector position on the selector track.
Torque transfer systems with transmission devices, including automated shift transmissions, belong to the known state of the art and are commercially available.
However, experience has shown that automated shift transmissions in particular are more prone to wear, which often causes components to fail prematurely. Also, in known devices the shift movements into certain positions are not performed with the degree of precision given by a control device.
It is therefore the object of the present invention to provide a method of operating a torque transfer system in a motor vehicle, and to provide a torque transfer system that is capable of operating in accordance with the inventive method, so that the precision of the shift movements is improved and the amount of wear is reduced in a cost-effective and technically non-complicated manner.
To meet the foregoing objective, the invention proposes a method of operating a torque transfer system in a motor vehicle. The torque transfer system includes a shifter device with a movable element that is movable into a plurality of shift positions, an actuator device to apply an actuating force to the movable element, a control device to control the actuator device, and a position-detecting device to detect a position of the movable element. The movable element is subject to a position-dependent force, and the shift positions coincide with minima of the potential energy of the position-dependent force. As a result, the movable element has a tendency to fall into the nearest one of the shift positions.
In a first step of the inventive method, an output signal is issued by the control device to the actuator device with the end purpose of moving the movable element to a targeted shift position or more specifically, to a position within a given first tolerance band of the target position. When the movable shifter element has arrived within a second tolerance band that is wider than the first tolerance band and contains the latter, the movement of the shifter element stops at least for a short time interval. The stop can be the result of two or more forces canceling each other at a specific point. Specifically, one of the forces is a position-dependent field force of a force potential, while at least one other of the forces is a holding force of the movable element that counterbalances the field force. Under the inventive method, the targeted shift position is located essentially at a point where the force potential has a local maximum or minimum, i.e., where the field force reverses its direction.
In a second step of the inventive method, a stall-releasing signal is generated by the control device in accordance with a predetermined characteristic, to overcome the holding force on the movable shifter element at least partially to allow the shifter element to move and to ensure that the shifter element settles at a final position within the first tolerance band of the targeted position.
In specific embodiments of the invention, the output signal is transmitted to the actuating device and the latter, in turn, applies a force to the movable shifter element or to a component that is coupled to the movable shifter element. The output signal may also consist of a sequence of two or more signals following each other.
The method can include detecting the position of the movable element or of the component that is coupled to the movable element. The detecting function can be performed by the position-detecting device. Preferably, the movement and position of the element are detected by way of other quantities, e.g., an electrical current or voltage. As soon as the movable shifter element has essentially attained the targeted shift position or arrived within a tolerance band of the target position, an output signal is generated by the control device to stop the movable shifter element for at least a short time interval.
A stop of the movable element in the sense of the present invention means that the velocity of the movable element in relation to the torque transfer system equals zero for at least a short time interval. A velocity of zero also includes a reversal of direction, where the velocity of the movable element changes from a positive to a negative value or vice versa.
The position-dependent field force or force potential is, at least in principle, not limited to any specific force-generating effect or device. Preferred is a force field or force potential that is generated by means of a mechanical spring. Preferred is a concept where the movable shifter element, or a component coupled to the latter, has a contour curve or contour surface. A push rod or other contact element is force-biased by a pre-tensioned spring against the contour curve. As the contour curve moves with the movable shifter element or component, the contact element glides or rolls in spring-loaded contact along the contour curve. In preferred embodiments, the element with the contour curve or contour surface is a shifter shaft or a component coupled to the latter. Preferably, the contour has indentations or depressions corresponding to predetermined shift positions of the transmission, so that the cooperation between the contact element and the contour curve tends to bias the movement towards the nearest depression of the contour.
The depressions in the contour correspond in particular to the positions of the gear levels and the neutral position of the transmission. When the spring-loaded contact element is at the lowest point of a depression in the contour, the potential energy of the spring is at a minimum, so that the biasing force exerted on the movable element or component (which is obtained as the first derivative of the potential energy) reverses direction at the deepest point of the depression.
With the foregoing concept, the movable shifter element can be set precisely at the targeted positions, usually the gear-level positions and the neutral position of the transmission, even if the actuator device has not moved the shifter element precisely to the targeted gear position. When the actuator device ceases to exert a force on the shifter element, the latter will on its own seek the nearest minimum of the spring force potential, i.e., the targeted gear position. However, under certain conditions, for example due to friction, the spring force between the contact element and the contour curve may not be sufficient to drive the shifter element to the position of minimum potential energy. The shifter element will be held in a non-relaxed state in which the spring force and an opposed holding force cancel each other, so that the shifter element will be stalled and not move to the precise target position.
To break out of the stalled condition and overcome the holding force, a signal is generated in accordance with a predetermined characteristic to produce a force on the shifter element. This stall-release signal can be generated by the control device. As a result of the stall-release signal and the force produced by it, the shifter element will move to the nearest precise position of minimum potential energy.
The invention has the advantage that it allows the transmission device to be moved into predetermined positions of minimum potential energy, i.e., force-free positions. Internal stress forces that may be caused by a stalled position of a shifter element at any point between the control device and the last element in the chain of mechanical components, i.e., the gears of a shift transmission, can be eliminated or neutralized by the method according to the invention. This reduces the wear on components of the transmission, so that the useful life of the transmission and its parts will be longer. In addition, the invention allows a highly accurate absolute adjustment of the position-detecting device.
An absolute adjustment in the present context means that a shifter element is moved to an absolute reference position within the shift gate arrangement either at the occurrence of certain events or at predetermined time intervals. With the shifter element at the reference position, the position detecting device is set to a predetermined value. The reference position is a uniquely defined shift position to which the shifter element can be moved without requiring the position-detecting device to be working precisely.
A preferred embodiment of the present invention consists of a method of performing an absolute adjustment based on moving a shifter element to a position corresponding to a local minimum of a potential energy field, i.e., a point where the field force reverses direction.
The invention allows absolute positions to be determined independent of temperature, load cycles, or other influence factors.
In a further embodiment of the invention, the method is somewhat simplified: In a first step, an output signal is generated by the control device to move the movable shifter element to a predetermined targeted shift position or at least close to the latter. In a second step, a release signal is generated by the control device in accordance with a predetermined characteristic, to overcome the holding force on the movable shifter element so that the latter will position itself in a tension-free rest position.
According to the invention a first output signal is generated according to a predetermined characteristic with the result that a movable element of the transmission is moved to a predetermined targeted shift position or at least close to it, specifically to a position within a preliminary or second tolerance band.
When the movable element has reached the target position or a point close to it, a second output signal is generated by the control device to push the movable element free of its preliminary, stalled position and into an essentially force-free rest position.
According to a preferred embodiment of the invention, the second signal or stall-releasing signal is issued only if the movable element is close to, but not precisely at, the targeted shift position. The position of the movable element is monitored by the position-detecting device.
According to a particularly preferred embodiment of the invention, the stall-releasing signal is issued also in cases where the position-detecting device indicates that the targeted shift position has been attained. Taking this measure will prevent in particular that the movable element will remain in a stalled condition at some distance from the targeted position if the position detecting device gives an erroneous signal that the movable element is in the targeted position when this is not actually the case.
According to a particularly preferred embodiment of the invention, a stall-releasing signal is issued if the movable element has been found to be at a limit stop that is close to the targeted shift position. Since all shift positions correspond to energy minima, the potential energy decreases from the limit stop towards the targeted shift position. The stall-releasing signal can have the effect that the movable element will follow the path of least resistance, i.e., of decreasing potential energy, to move to the targeted shift position. In particular, the force produced as a result of the stall-releasing signal may overcome the holding force that opposes the minimum-seeking force of the potential energy field.
Also among the highly preferred embodiments is a concept to ascertain that if the movable element is found at a limit stop, this condition is intended, i.e., not due to a stalled condition of the movable element.
Further among strongly preferred embodiments of the invention is a concept where the value of a predetermined characteristic parameter is monitored and/or evaluated and a stall-releasing signal is generated dependent on the predetermined characteristic parameter or the time profile of the characteristic parameter. The characteristic parameter is in particular a parameter of the transmission device or of the clutch device, or a parameter of the motor vehicle in general. In particular, the parameter is an operating parameter whose value can change during operation of the vehicle or of the transmission device or clutch device.
With particular preference, the characteristic parameter is an electric parameter such as an electric current or voltage.
In a preferred embodiment of the invention, the control device sends an electrical signal to the actuator device which, in response, applies a force to the shifter device. In particular, the electrical signal consists of an electrical voltage that is applied to the actuator device. With special preference, the actuator device works with a selector motor and a shift motor, and the control device applies voltages to these two motors which will be referred to herein as selector voltage and shift voltage. As a consequence of the selector voltage and shift voltage, corresponding currents will flow in the respective motors. In addition, an overall total current can be defined as the current that flows from the control device to the actuator device.
With particular preference, at least one of the currents is monitored against a voltage that is set by the control device (voltage controlled method). The voltage set by the control device can be a constant voltage, or it can be variable according to a predetermined characteristic.
With a voltage-controlled process, it is preferred according to the invention to monitor the electric current as a function of time. The current that is monitored is the sum total of the current supplied by the control device and/or the current supplied to the selector motor and/or the current supplied to the shift motor, and/or some other current of the transmission device. A particular purpose of monitoring a current is to determine from the current fluctuation over time if a movable element of the actuator device or the shifter device changes its impedance to the current. As a result of the variable impedance, the movable element may move at different speeds even if the opposing mechanical force is the same. A change in impedance can also be caused by a mechanical limit stop or by the absence of a limit stop.
When the movement of the movable element is opposed by an increasing mechanical resistance, this will manifest itself through an increase in the actuating current, while a decreasing mechanical resistance will manifest itself through a decrease in the actuating current. The fact that the movable element has reached a limit stop may be recognized from a strong increase in current. Projections and depressions in the surface contour of the movable element that interacts with the spring-loaded contact element manifest themselves through local maxima and minima in the profile of the electric current.
According to the invention, local minima (representing depressions in the surface contour) are correlated to the gear levels and the neutral position of the transmission. In other words, a position where the contact element is at the bottom of a depression in the surface contour corresponds to one of the gear levels or the neutral position of the transmission.
When the movable shift element or a component coupled to the latter is approaching a gear level position or the neutral position and is within a predetermined range of the exact position, this can be recognized from the change in the current signal.
With preference, a stall-releasing signal is generated after the monitored characteristic quantity (i.e., the current) has increased or decreased longer than a predetermined time interval and/or by more than a predetermined amount, and after it has been ascertained that the movable element is at least close to the targeted shift position. The purpose of ascertaining that the movable element is at least in close proximity to the targeted shift position is to prevent that a minimum in the current profile is correlated with an incorrect gear position.
The aforementioned ascertainment can be realized in a variety of ways, e.g., by means of a position-detecting device or by long-term monitoring of the current signals.
According to a preferred embodiment of the invention, a stall-releasing signal is generated after detecting that the monitored quantity, i.e., the monitored current, has passed through a local minimum. Preferably, this includes a check that the minimum has not already been followed by a maximum.
Preferably, the position of the movable element is monitored by a position-detecting device, and a stall-releasing signal is generated if the position-detecting device indicates that the movable element is at least in the proximity of the targeted shift position.
According to a particularly preferred embodiment of the invention, a stall-releasing signal is generated if the movable element is in the proximity of the targeted shift position but not at the precise local minimum of the potential energy field, or if the contact element is not at a local minimum of the surface contour.
Immediately after the stall-releasing signal, an actuating force is applied to the movable element in the opposite direction of the force that was driving the element prior to the stall-releasing signal. However, the range of preferred solutions also includes applying at least initially an actuating force in the same direction as the force that was driving the movable element prior to the stall-releasing signal.
Preferably, the stall-releasing signal has the effect that the movable element is subjected at least initially to an actuating force in the direction towards the targeted shift position. The direction from the current position of the movable element towards the targeted shift position can be determined from the time profile of the current or by means of a position-detecting device.
If the movable element is found stalled in a position close to a limit stop, it is preferable to at least initially apply a force that is directed away from the limit stop.
With particular preference, an output signal is generated to move the movable element towards a limit stop, in particular towards an end stop of a shift track. The condition where further movement of the movable element is blocked by the end stop can be detected from the time profile of the current or by means of a position-detecting device. Subsequently, a stall-releasing signal is generated to apply a force to move the element away from the end stop.
Preferably, the stall-releasing signal is substantially not a pulse signal. Specifically, the signal consists of a voltage that stays constant for a predetermined time interval or until a predetermined event occurs, or it can be variable over time in accordance with a predetermined characteristic. With preference, the stall-releasing signal is a signal other than a pulse, causing a small amount of force to be applied to the movable element. In particular, the force can be of a magnitude between zero and double the amount of holding force by which the further movement of the moving element has been opposed. Preferably, the stall-releasing signal is set at least part of the time at a level where the force on the movable element corresponds substantially to the holding force or is smaller than the holding force by which the movement of the element is being opposed.
Preferably, the stall-releasing signal is a voltage other than a pulse that is applied to an electric motor or other element of the actuating device, of a magnitude between 0.3 volt and 2.5 volt, preferably between 0.4 volt and 1.7 volt, and with special preference between 0.5 volt and 1.5 volt.
The stall-releasing signal can at least reduce the magnitude of inherent holding forces that may be due, e.g., to the holding torque of an electric motor used for the shifter and/or selector actuation, or other holding forces acting on a movable element of the actuator or shifter device.
According to a particularly preferred embodiment of the invention, the stall-releasing signal that is applied to an electric motor used for the shifter and/or selector actuation is a voltage other than a pulse, and is less than the minimum voltage required to cause the motor to move.
In other preferred embodiments, the signal is a pulse signal.
The pulse signal can have a plurality of successive pulses of alternating polarity.
The pulsed stall-releasing signal has the effect that the movable element is subjected to one or more forces of substantially alternating direction.
With preference, the pulsed stall-releasing signal consists of voltage pulses.
The voltage pulses and the force pulses generated by them can be of equal or different magnitude and of equal or different length. The pulse repetition time, i.e., the time between two consecutive pulses or the period between two identical pulses can be constant or variable.
Preferably, the voltage pulses that immediately follow each other have opposite polarity and identical duration. The generation of the stall-releasing signal is maintained until a predetermined characteristic value moves back and forth between a first position and a second position.
The aforementioned characteristic value can be the shift position or the speed of movement of a movable element of the shifter device or actuator device. The value can also be the magnitude of a current such as the total current flowing in the control device or in the actuator device, or the current of a motor of the shifter and/or selector actuation. In particular, the back-and-forth movement between the first and second postion occurs in such a manner that at least one of the two positions is attained at least twice in succession. It is particularly preferred if the characteristic value as a function of time reaches a lower first position, then a higher second position, then the same first position again. Also among the preferred possibilities, the characteristic value as a function of time may run from a higher first position to a lower second position and back again to the higher first position. It is particularly preferred to keep generating the stall-releasing signal until the predetermined characteristic value has attained the same high position at least a first number of consecutive times and the same low position at least a second number of consecutive times, with the first and second number being either equal or different by one count. Further among the preferred possibilities, the alternating stall-releasing signal is kept up until the characteristic value as a function of time has alternatingly attained the same high and low positions for at least a predetermined length of time.
According to the inventive method, as soon as the characteristic value as a function of time runs back and forth symmetrically in the manner described above, this is interpreted as an indication that the movable element or a component coupled to it is in a substantially force-free or non-stalled shift position.
With preference, the pulsed stall-releasing signal consists of voltage pulses of alternating polarity in which the product of voltage and pulse duration is determined according to a predetermined characteristic. The predetermined characteristic in this case is in particular a function of a predetermined characteristic value such as a friction force or a coefficient of friction.
Preferably, the pulses are generated at a high frequency.
Also as a preferred concept, the position-detecting device detects and/or monitors the position of the movable element or a component coupled to the element during the time when the stall-releasing signal is in effect.
According to a preferred embodiment of the invention, the position-detecting device is checked or adjusted or adapted under predetermined conditions at a time when a predetermined targeted shift position has been attained after a stall-releasing signal, i.e., when the movable element is in a substantially force-free or non-stalled position.
A particular embodiment of the inventive method of operating the torque transfer device is designed as an emergency strategy that is initiated under certain conditions and under which the movable element is moved successively to different predetermined target positions identified by a running index k that is incremented from 1 to n in steps of 1. At each of the n target positions, the inventive method is used according to one or more of the embodiments described above. The same embodiment of the invention may be used identically for all of the shift positions, or different embodiments or versions of the inventive method may be correlated with the different positions.
Further included in the scope of the invention is a torque transfer system that is configured with the required capabilities to perform the inventive method according to any of the embodiments or versions of the method as described herein.
Also included in the scope of the invention is any method of operating a motor vehicle that includes utilizing the method or torque transfer system of the present invention.
As a linguistic formality, where the names of features are connected by the word xe2x80x9corxe2x80x9d, this should be understood in the broadest sense, i.e., either as a logic type of or (one or the other or both) or an exclusive or (one or the other but not both), whichever fits the context.
The terms xe2x80x9ccontrolxe2x80x9d and xe2x80x9cregulationxe2x80x9d and their derivatives are used herein with a broad range of meanings encompassing closed-loop as well as open-loop control of devices, functions and processes, including in particular the DIN (Deutsche Industrie-Norm) definitions for regulation and/or control).
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. The inventive method itself, however, both as to its mode of operation and its application in a motor vehicle, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.